Question mini itx system not powering up ?

Oct 25, 2020
mini itx system power failure

I have an ASRock z170 mini itx system with a Streacom f7c chassis that I put together around 5 years ago which has worked perfectly fine ... until it was moved a few days ago.

After moving the system around 6 feet within the same room and reconnecting the cables to the same power supply, the PC seemed perfectly fine to begin with. I was also able to add a (new Viewsonic) second monitor (the m/b has 2 hdmi connections and 1 display port), and everything seemed well.
So I had one monitor (the original) on dp connection, the new one on hdmi, both working fine for 10 minutes or so.

However, after more disconnecting, rearranging position of monitors and reconnecting, pressing the Power On button suddenly had no effect, and the PC seemed dead - no light on the front panel - nothing.
After several attempts (including holding down the Power button and draining the power supply - this had worked in the past when occassionally the PC wouldn't boot up), I decided to disconnect all the hardware (monitors, printers etc...)
Initially, this had no effect, but after about 3 goes and giving the system half and hour's rest, the PC (no peripherals connected) powered up again (as normal).
However, when I connected everything back, the system did not work.
On disconnecting the peripherals again, the PC unit was completely dead.

I then opened up the f7c chassis and tried a new Power unit that I had in reserve (thinking that the previous one must be faulty), and on first connection (peripherals attached) everything seemed fine again.
However, second time round, the system would not start.
After disconnecting the peripherals again, there was a spark (a bit like you get when you connect jump leads to a car battery, only about a tenth of the scale) when I connected the new Power supply unit to the Streacom chassis, and since then the PC has been completely dead.

Any thoughts?
Do you think this has anything to do with the second monitor being connected to the back of the PC unit i.e. some sort of faulty connection to the motherboard?
Or is the addition of second monitor just a coincidence, and that the real problem might be something else e.g. faulty on'off button/wiring, power supply?

I'm really concerned about the spark, why it occurred, and any damage it might have caused.

I have another system with the same set up (extra monitor added but no printer, scanner), but so far that seems to be fine.

Any help appreciated.